A coal seam fire or mine fire is the underground smouldering of a coal deposit, often in a coal mine. Such fires have economic, social and ecological impacts. They are often started by lightning, grass, or forest fires, and are particularly insidious because they continue to smoulder underground after surface fires have been extinguished, sometimes for many years, before flaring up and restarting forest and brush fires nearby. They propagate in a creeping fashion along mine shafts and cracks in geologic structures. Because they burn underground, coal seam fires are extremely difficult and costly to extinguish.
There are many subterranean coal seam fires around the world: in USA, Australia, South Africa, China, India and other counties. Some of these fires are burning for more than 50 years and may continue burning yet hundreds of years. The temperatures can exceed 1000° C. Enormous quantities of toxic gases and heavy metals may be thrust up to atmosphere, resulting in damaging the environment.
In order to thrive, a fire requires fuel, oxygen, and ignition or heat. As underground fires are very difficult to reach directly, firefighting involves finding an appropriate methodology which addresses the interaction of fuel and oxygen for the specific fire in question. In Pennsylvania, GAI estimated it would cost upward of $600 million to completely dig out the fire. Energy can be removed by cooling, usually by injecting large amounts of water. However, if any remaining dry coal absorbs water, the resulting heat of absorption can lead to re-ignition of a once-quenched fire as the area dries. Accordingly, more energy must be removed than the fire generates. In practice these methods are combined, and each case depends on the resources available. This is especially true for water, for example in arid regions, and for covering material, such as loss or clay, to prevent contact with the atmosphere.
This disclosure relates to the field of environment protection from toxic gases and heavy metals generated by existing subterranean coal seam fires and by-products utilisation.
Coal seam fires may cause strong environmental pollution, social and economic disaster in the areas of fire, land subsidence and enormous cost. In some cases, firefighting methods may be employed in an attempt to quench the fire. However, conventional firefighting techniques may not be effective for extinguishing the fire. In other cases, the fire may simply be abandoned. This, of course, is not a solution to the problem.
Some Related Patents/Publications
The following patents and publications may have some relevance to the techniques disclosed herein, and are incorporated by reference herein.
U.S. Pat. No. 7,464,992 (2008 Dec. 16; Ozment) discloses a method for forming a barrier by forming a barrier to seal off a remote chamber that is involved in a fire and which permits access to the area involved in a fire for additional remote firefighting operations. A conduit is then introduced through the borehole. Next, through the conduit, a flowable barrier material is introduced to the area to be sealed. More particularly, Ozment discloses                a method for forming a barrier to seal off a remote chamber including the steps of: forming a borehole that communicates between a first location and the remote chamber; inserting a conduit through the borehole to extend into the remote chamber; introducing a flowable material through the conduit to the remote chamber and dispensing the flowable material from the conduit to the desired location for the barrier, the flowable material upon being dispensed producing a substantially solid, self-sustaining composition; maintaining dispensing the flowable material to produce a sufficient quantity of the self-sustaining composition to form the barrier to seal the remote chamber, while ensuring that the composition does not block the borehole from communicating between the first location and the remote chamber; and thereafter removing the conduit to allow access to the borehole. (Abstract)        Generally described, the method provides a borehole that opens into the remote chamber and proximate the point at which a seal is to be formed. A conduit is then introduced through the borehole. Next, through the conduit, a flowable barrier material is introduced proximate the area to be sealed. After the barrier is formed, the conduit can be removed, so the borehole remains open for access to the fire involved area. (Summary)        More specifically described, the conduit is a pipe or hose and has an elbow to direct the flow of the flowable material. The flowable material has a first component and a second component. The components are mixed with each other just prior to dispensing from the conduit to the point at which the seal is to be formed. The first component may be a urethane, phenolic, or epoxy and the second component is an activator to react with the first component to produce a foam that expands and forms a barrier that is a substantially solid, self-sustaining composition. (Summary)        
Ozment's technique can be used in a confined are to seal off a remote chamber by forming a barrier from foam. This will be not practical to stop underground fire expansion of coal seam. Ozment's method will not generate capital (revenue) during creation of barrier.
U.S. Pat. No. 5,909,777 (1999 Jun. 8; Jamison) discloses method and apparatus for stopping the spread of a fire in an underground mine. More particularly, Jamison discloses                An assembled length of water pipe sections having a nozzle pipe section at an inby (inlet) end is moved from a crosscut of a mine into a mine entry to stop the advance of a fire in the entry without requiring firefighters to be positioned in the fire entry. The nozzle pipe section is moved across the entry to a position adjacent to an opposite entry sidewall. The nozzle pipe section is connected at an outby (outlet) end in the crosscut by assembled sections of extension water pipes to a water feedline. Water under pressure is supplied through the extension pipes to the nozzle pipe section and discharged from the nozzles to generate a series of intersecting sprays directed at selected angles in a range between about 0-90.degrees in the entry, forming a water curtain the complete height and width of the entry. Deflected water sprays from the sidewalls and mine roof combine with the upward water sprays to form a curtain of water extending across the path of the advancing fire and into contact with roof bolts supporting the mine roof above the entry. The water spray prevents the roof bolts from being heated to an elevated temperature which can cause a loss of anchorage of the bolts in the mine roof. The water curtain also cools the hot gases generated by the fire to stop advance of the fire beyond the curtain so that the fire can be contained and extinguished. (ABSTRACT)        
Using water to quench a seam fire, hydrogen may be generated at high temperatures, thereby adding fuel to the fire. Jamison's method can work inside mine on small areas at low temperatures, but if some coal will remain dry, then the coal will start burning again. Installation of such piping system toterminate underground seam fire may not be practical.
U.S. Pat. No. 8,397,829 (2013 Mar. 19; Brown) discloses a method and apparatus for controlling and extinguishing subterranean coal fires. Suitable detection and measuring devices are initially used to determine the extent of the fire and develop a plan of extinguishment. Flow control devices are added to all the mine's access points in order to control gas flow into and/or out of the mine. In addition, new access points may be added. Gaseous carbon dioxide is pumped into the mine until a positive pressure is developed (with respect to atmospheric pressure. Pressurized and liquefied carbon dioxide is directed into the area of the combustion face. The liquid carbon dioxide blankets the combustion area with a gas which will not support combustion and absorbs a tremendous amount of heat from the burning coal.
If gas will not be able to intrude in to some isolated voids in the coal—and in a coal seam there may be numerous such voids—then the fire will start again.
Some other patents of interest may include,                US 20100218507(2010 Sep. 2; Cherson) which discloses an apparatus and method for capturing, separating, transforming, and sequestering carbon wherein said apparatus dissociates a carbon containing feedstock material and reacts the resulting gases with a system-produced brine to create four products: 1) a sodium based carbonate or bicarbonate, 2) ammonium chloride, 3) fresh water, and 4) a multi-purpose building material. End product (1) may be sequestered in any of several ways for durable and long term storage. End product (2) may be used for nutrient enrichment. End products (3) and (4) may be distributed to human populations.        EP 1853358 (2013 Aug. 5; Schaefer) which discloses fire fighting foam concentrate, an expanded foam composition and a process of forming a foam composition concentrate, aqueous foaming compositions containing carbonised or caramelised saccharides. The foaming compositions are most preferably biodegradable and/or environmentally compatible.        
Some shortcomings of existing techniques for combating coal seam fires may include:                Sealing the chamber by forming a barrier from “flowable” material means that only space which is empty will be filled. If flammable materials, such as coal, remain in the walls or ceiling of the space (chamber), the probability of new fire occurring is very high.        Providing a conduit (or borehole) for introducing “flowable” material is an imperfect solution in that the borehole will remain opened to air after completion of the firefighting operation, in which case new fire ignition of the coal seam may be highly possible. This method may be used only as a temporary solution.        Sealing the chamber with solid materials may render the mine difficult to re-open.        
Ideally, a technique for terminating a coal seam fire, or the spread (extension) thereof would permit access to the coal seam and would allow resuming mining operations once the fire has been appropriately dealt with.
Underground Coal Gasification
Underground coal gasification (UCG) is an industrial process which converts coal into commercialproduct—Syngas. UCG is an in-situ gasification process carried out in non-mined coal seams using injection of oxidants, and bringing the product gas to surface through production wells drilled from the surface.
The predominant product gases are methane, hydrogen, carbon monoxide and carbon dioxide. Ratios vary depending upon formation pressure, depth of coal and oxidant balance. Gas output may be combusted for electricity production. Alternatively, gas can be used to produce synthetic natural gas. Hydrogen and carbon monoxide can be used as a chemical feedstock for the production of fuels (e.g. diesel), fertilizer, explosives and other products. Carbon Dioxide may be pumped into a coal seam for sequestration and increasing coals calorific value. UCG offers an alternative to conventional coal mining methods for some resources.